1. Field of the Invention
The invention relates to a method for the production of tools for a chip-removing machining of metallic materials.
Furthermore, the invention relates to chip-removing tools.
2. Discussion of Background Information
Tools made of alloyed steel, in particular high-speed steel, with a chemical composition in % by weight of
Carbon (C)0.7 to 1.3Silicon (Si)0.1 to 1.0Manganese (Mn)0.1 to 1.0Chromium (Cr)3.5 to 5.0Molybdenum (Mo) 0.1 to 10.0Tungsten (W) 0.1 to 19.0Vanadium (V)0.8 to 5.0Cobalt (Co)up to 8.0as well as aluminum, nitrogen, iron and impurity elements as remainder, are essentially known.
For example, in GB 2 096 171 A, high-speed steel alloys are proposed having an elemental content of vanadium, tungsten, and molybdenum to exceed a total of 2% by weight, wherein in a further development of the invention, the concentration of silicon plus aluminum is to be adjusted below a maximum value of 3.5% by weight. An advantageous effect on the tool properties is to be achieved by these measures, which effect otherwise appears to be achievable only by means of cobalt.
According to US 2006/0180 249 A1, it has been proposed to alloy a low-alloyed high-speed steel (C=0.5-0.75% by weight, Cr=5.0-6.0% by weight, W=0.5-2.0% by weight, V=0.7-1.75% by weight) with aluminum up to 0.1% by weight and nitrogen up to 0.04% by weight, wherein the Mo equivalent is to be 2.5-5.0% by weight and the Mo equivalent/vanadium content value is to be 2 to 4.
U.S. Pat. No. 6,200,528 B1 discloses a high-speed steel alloyed in a complex manner, which can advantageously be produced with a special oxidation method. This material, which is to have improved high-temperature properties, is alloyed with 0.03 to 1.25% by weight aluminum and has nitrogen contents from above 0.03 to above 0.04% by weight.
Most of the proposed tool steels alloyed with aluminum, in particular the high-speed steels, are not used for production of cutting tools. Although it is true that there are indications that individual specific tool properties can be influenced favorably by aluminum content in the steel (for example, where applicable, aluminum content of up to 2% by weight), a desired quality assurance and an overall high quality profile of the tool do not appear to be present to a sufficient extent or not in a convincing manner. In other words: in modern machining facilities, the tool is exposed simultaneously to a number of stresses, including high mechanical tribological and wear stresses due to the work technologies provided, as well as elevated temperature, wherein a failure in only one type of stress requires tool replacement that is expensive, at least from the point of view of cost effectiveness.
In practical use, tools alloyed with aluminum are used only to a small extent, probably also for reasons of possible uncertain quality.
It is known to the person skilled in the art that aluminum contents in steel strongly cut into the gamma region in the equilibrium diagram.
Carbon in iron/aluminum alloys expands the gamma region. However, the solubility for carbon in γ-mixed crystal is reduced by aluminum.
According to the technical literature, aluminum contents in tool steel can contribute to the fine-grain formation of the material due to nitride precipitations. However, a hardening depth into the piece can be sharply reduced by thermal hardening and tempering treatment.
With high-speed steels, titanium- and/or tantalum- and/or niobium additives are frequently recommended in textbooks in addition to the alloying elements of chromium, tungsten, molybdenum, and vanadium, in order to be able to use a higher hardening temperature in the hardening and tempering of the tool with aluminum and nitrogen, or to minimize its susceptibility to overheating due to coarse grain formation.
According to a large number of expert opinions, aluminum in high-speed steel can only possibly reduce the fretting phenomena on the surface of the tool and have a favorable effect with respect to cratering.
From a comprehensive critical examination of a large number of prior art documents as well as research results, no unambiguously certain indications concerning the effect of aluminum in tool steels can be found. Reasons for a premature failure or a disclosed longer service life of a tool alloyed with aluminum are not known to the person skilled in the art.
General research has shown that as the contents of elements of group 4 and 5 of the periodic table (IUPAC 1988) and carbon rise in tool steel, in particular in high-speed steel, the proportion of monocarbides therein rises and in this way the wear resistance of the tool material can be improved. However, the material toughness is considerably reduced thereby in a disadvantageous manner due to coarse carbide formation, so that the danger of breakage and chipping of the tool is increased.
Moreover, contents of vanadium as an important monocarbide-forming element up to approximately 5% by weight in the presence of elements of group 6 of the periodic table (IUPAC 1988), in particular of molybdenum up to 10% by weight, optionally of tungsten up to 19% by weight and chromium up to 6% by weight in the tool steel, cause only a few hard wear-resistant monocarbides. The chief proportion of carbide in the hardened tool is present essentially as mixed carbides of the Me2C and Me6C types, which have a lower abrasion resistance than monocarbides.